1. Field of the Invention
This invention relates to an apparatus for manufacturing an internal grooved tube (a heat exchanger tube) having multiple axial-directional or spiral parallel grooves formed in the internal surface.
2. Description of the Prior Art
Referring to FIG. 4, a conventional apparatus for manufacturing an internal grooved tube will be described.
A rotary die 2 having a cylindrical cover 21 and a working head 3 integrally coupled to the rotary die 2 are provided in order at the upstream side along the drawing direction of a metal blank tube 1a. 
The working head 3 has a conical internal surface which becomes wider toward the downstream side in the drawing direction. Aligned inside the working head 3 are a plurality of balls 6 positioned at equal intervals around the metal blank tube 1a which turns in contact with the internal surface and passes inside the working head 3. Those balls 6 are pressed toward the upstream side in the drawing direction by a flange-shaped stopper 31 attached to another member through a bearing 32 at the downstream side.
A shaping die 7 is provided further downstream of the working head 3 in the drawing direction.
A lubricating-oil feeding unit 22 which feeds a lubricating oil to the outer surface of the metal blank tube 1a is provided downstream of the cover 21 in the drawing direction.
At the time the manufacturing apparatus is operated, as shown in FIG. 4, the metal blank tube 1a is put through the rotary die 2, the working head 3 and the shaping die 7, and a plug 4 and a grooved plug 5 rotatably coupled to the plug 4 through a plug rod 51 are inserted in the metal blank tube 1a. While the metal blank tube 1a is drawn rightward in the figure, the rotary die 2 and the working head 3 are rotated together by unillustrated same drive means. Multiple spiral grooves (projections) having a predetermined lead angle with respect to the axial direction are formed in parallel on the outer surface of the grooved plug 5.
Through the above-described operation of the apparatus, the diameter of the metal blank tube 1a is reduced by the rotary die 2 and the plug 4. Then, the metal blank tube 1a is pressed against the outer surface of the grooved plug 5 at the position of the grooved plug 5 by the plural balls 6 which rotates with play while revolving around the metal blank tube 1a in accordance with the rotation of the working head 3, and multiple fine grooves 10 are formed on the internal surface of the metal blank tube 1a, thus producing a tube 1 with a grooved internal surface. The internal grooved tube 1 is shaped while its diameter is reduced by the shaping die 7.
During the operation of the apparatus, the lubricating-oil feeding unit 22 supplies the lubricating oil to the outer surface of the metal blank tube 1a. The lubricating oil is supplied to a work portion in the rotary die 2 through the outer surface of the metal blank tube 1a that is moved in the drawing direction and is also supplied to a work portion in the working head 3 through a plurality of oil passages 23 formed toward the interior of the working head 3 from a position closer to the outer portion than a drawing hole of the rotary die 2.
The apparatus for manufacturing an internal grooved tube is designed in such a way that the rotary die 2, not a fixed die, which rotates in the aforementioned manner, is placed upstream in the drawing direction and the drawing resistance is decreased by changing the direction of friction between the metal blank tube 1a and the rotary die 2 at that portion (the direction of friction being inclined to the drawing direction), thereby reducing the drawing load applied to the metal blank tube 1a. 
An apparatus for manufacturing an internal grooved tube according to the present invention comprises a rotary die, a plug inserted in a metal blank tube which is put through the rotary die and drawn therefrom and performs a diameter-reducing work on the metal blank tube together with the rotary die, a grooved plug which is rotatably coupled onto the axial line of the plug in the direction of the distal end thereof through a plug rod and has multiple axial-directional or spiral grooves formed in the outer surface, and a working head which is provided in such a way that the metal blank tube passes inside at the position of the grooved plug and rotates independently of the rotary die. A conical internal surface which becomes wider in the drawing direction of the metal blank, tube is formed inside the working head.
A plurality of balls are retained inside the working head in such a way as to rotate in contact with the outer surface of the metal blank tube and the conical internal surface and to be pressed against the outer surface of the grooved plug through the metal blank tube. The individual balls are constructed in such a way as to revolve on the same circular orbit about the metal blank tube as the working head rotates.
A first lubricating-oil feeding unit which feeds a lubricating oil to a work portion of the rotary die is provided upstream of the rotary die in the drawing direction of the metal blank tube. Further, a second lubricating-oil feeding unit which feeds a lubricating oil to the surface of the metal blank tube which passes inside the working head is provided downstream of the rotary die in the drawing direction and upstream of the working head in the drawing direction.